This power supply was developed and designed by Power Engineering Department for national basic scientific project BEPCII (Beijing Electron Positron Collider upgrade and expansion project), which is undertaken by the Institute of High Energy Physics, Chinese Academy of Sciences. The superconducting magnet power supply and quench protection circuit in collision area will be used in the protections of excitation and after quench for superconducting magnet installed inner spectrometer of storage ring. The overall technology of this equipment (including superconducting magnet, power supply and quench protection circuit) is first practically applied in high-tech field in China. Superconducting magnet power supply and quench protection circuit is one of the most critical equipment for collider.